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Optimizing the Combobox

The best approach to optimize the performance speed of Telerik RadComboBox when using huge amount of items is using the load-on-demand feature.The load-on-demand mechanism loads the items only when the user types or clicks in the field or the drop-arrow image. You can also load the items only upon clicking on the drop arrow. To do this you should set the ShowDropDownOnTextboxClick property to false. For even faster load of the page, you can leave the combobox empty when it is first rendered on the page. Items will be added as soon as the user clicks in the input field, the drop-arrow image or types some text into the input field. In other words, you can add the items only in the ItemsRequested event handler or via WebService.

When using the load-on-demand mechanism with ItemsRequested event you should:

  1. Set the EnableLoadOnDemand property to true.

  2. Subscribe to the ItemsRequested event and add the items there.

<telerik:RadComboBox RenderMode="Lightweight" 
    id="RadComboBox1" 
    runat="server" 
    EnableLoadOnDemand="true" 
    OnItemsRequested="RadComboBox1_ItemsRequested">
</telerik:RadComboBox>

protected void RadComboBox1_ItemsRequested(object o, Telerik.Web.UI.RadComboBoxItemsRequestedEventArgs e)
{
    RadComboBox1.Items.Add(new RadComboBoxItem("item 1", "1"));
    RadComboBox1.Items.Add(new RadComboBoxItem("item 2", "2"));
}


Protected Sub RadComboBox1_ItemsRequested(ByVal o As Object, ByVal e As Telerik.Web.UI.RadComboBoxItemsRequestedEventArgs) Handles RadComboBox1.ItemsRequested
    RadComboBox1.Items.Add(New RadComboBoxItem("item 1", "1"))
    RadComboBox1.Items.Add(New RadComboBoxItem("item 2", "2"))
End Sub

ShowMoreResultsBox and EnableVirtualScrolling

When you load the combobox items from heavy database, you can cache the data source so that additional calls are avoided. This will make the combobox event faster.

A sample project can be seen here: Load On Demand

See Also